As the scale of drilling in oil and gas fields is increased and science and technology are developed continuously, especially, as logging while drilling (LWD) techniques are developed rapidly, there is an urgent need for state-of-the-art science and technology to play an important role in oil and gas field exploitation. The acoustic LWD technique is one of the LWD techniques, and acoustic receiving transducers while drilling are the most important elements of an acoustic LWD instrument. When the LWD instrument operates, acoustic waves are generated by an emitting transducer built in the instrument, and then the acoustic waves are received by receiving transducers in the same instrument. The properties of the specific medium are evaluated according to the received acoustic information, i.e., velocity and attenuation of the waves in different modes. In view that there is a water passage through which the mud can flow in the middle of the LWD instrument, the acoustic transducers are installed on the outer wall of the drill collar, and it is difficult to seal the acoustic transducers by immersing them in oil just like in the case of a cabled acoustic logging tool. Therefore, conventionally, acoustic receiving transducers while drilling are usually packaged separately. Presently, there are two types of matured acoustic receiving transducers while drilling: button-type receiving transducers and annular packaged receiving transducers. A button-type receiving transducer is directly installed in an electronic compartment at the receiving side of an acoustic LWD instrument, and such a transducer has relatively high downhole receiving sensitivity. In an annular packaged receiving transducer, multiple receiving transducers are packaged in an annular band structure, and the receiving chips are connected in shunt internally to constitute a receiving transducer. Such receiving transducers are mainly used in monopole acoustic LWD instruments.
The existing technical schemes are as follows:
Packaging device for button-type receiving transducers: in a transducer in such a structure, a ceramic crystal is packaged in a button-type metal structure, and balance between the mud outside the ceramic crystal and the hydraulic oil inside the ceramic crystal is realized by means of a hydraulic balance device in the button-type metal structure; the ceramic crystal must be dynamically sealed in the button-type structure, i.e., the pressure of the mud outside the ceramic crystal and the pressure of hydraulic oil inside the ceramic crystal should be balanced. The button-type receiving transducer is directly mounted to the frame of a receiving electronic compartment, and the electronic compartment is sealed against the external mud by means of a seal ring outside the button-type structure; at the same time, the twin-core electrical connecting contact pins on the bottom of the transducer are short-connected with a receiving circuit, and thereby weak acoustic signals can be received.
Packaging device for annular packaged receiving transducers: the transducer in such a structure employs a plate-type ceramic crystal structure, the receiving chips are packaged in an annular band, and the receiving chips are connected in shunt internally to form a receiving transducer. The signal receiving wires of the chips are led out of the annular band structure via a sealed structure, and the two signal receiving wires are electrically connected to the internal electronic compartment via a sealed electrical connecting plug that is specially designed. Such transducers encapsulated in epoxy resin can be immersed in the mud, the internal electronic compartment is sealed against the external mud by means of a specially designed sealed electrical connecting plug, and thereby weak acoustic signals can be received.
The existing technical schemes have the following drawbacks:
The packaging device for button-type receiving transducers causes increased complexity in transducer design because of the requirement for dynamic hydraulic pressure balance design of the ceramic crystal; besides, the structure may fail easily in the application; the ceramic crystal of the button-type transducer is exposed in mud and may be damaged easily in a complex downhole application environment, though a layer of PEEK material is bonded on the external surface of the ceramic crystal; in view that high-pressure sealing with the drill collar is implemented for the transducer while the transducer is mounted in the frame of the internal electronic compartment, such a structure causes increased requirements for the manufacturing and assembling of the frame of the internal electronic compartment and the external drill collar.
The packaging device for annual packaged receiving transducers requires a specially designed sealed electrical connecting plug to electrically connect to a power connection plug on the internal electronic compartment while implementing high-pressure sealing; in addition, the plug shall be secured to the drill collar in view that strong shocks and vibrations exist in the downhole operating environment. On one hand, the packaging structure requires a specially designed sealed plug; on the other hand, the packaging structure also causes increased requirements for the manufacturing and assembling of the frame of the internal electronic compartment and the external drill collar. Furthermore, compared with the packaging structure for button-type transducers, the packaging structure causes increased length of the electrical connecting wires from the transducer to the electronic compartment, and has adverse effects to signal pick-up.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.